Process for working up steel slags and iron carriers for obtaining pig iron and environmentally safe slags

Abstract

In a process for working up steel slags and iron carriers such as, e.g., electric furnace slags, converter slags, fine ores, dusts from steel production, mill scales for obtaining pig iron and environmentally safe slags, the volume ratio of molten slag to iron bath is chosen to be larger than 0.5 to 1 and, preferably, 0.8:1 to 1.5:1 and the slags are supplemented with SiO 2 carriers such as, e.g., foundry sands, metallurgical sands and/or fine ores so as to adjust a slag basicity (CaO/SiO 2 ) of between 1.0 and 1.8 and, preferably, 1.2 and 1.8 at an Al 2 O 3 content of between 10 and 25% by weight, based on the slag. In doing so, hot blast is top-blown and coal, optionally along with an inert gas and, in particular, nitrogen and, furthermore, optionally oxygen or hot air is blown through the iron bath.

What is claimed is:  
     
       1. A process for working up steel slags and iron carriers comprising at least one member selected from the group consisting of electric furnace slags, converter slags, fine ores, dusts from steel production, mill scales for obtaining pig iron and environmentally safe slags, comprising 
       forming a slag and iron bath suspension by thorough mixing of molten slag with an iron bath,  
       wherein the volume ratio of molten slag to iron bath is chosen to be larger than 0.5 to 1,  
       adding to the slag and iron bath suspension SiO 2  carriers comprising at least one member selected from the group consisting of foundry sands, metallurgical sands and fine ores so as to adjust a slag basicity of between 1.0 and 1.8 at an Al 2   O   3  content of between 10 and 25% by weight, based on the slag,  
       top-blowing hot blast,  
       blowing through the iron bath coal, optionally along with an inert gas, and, optionally oxygen or hot air is also blown through the iron bath, and  
       wherein the process is carried out in a converter with submerged tuyeres.  
     
     
       2. A process according to claim  1 , wherein the slag basicity is adjusted to between 1.3 and 1.6. 
     
     
       3. A process according to claim  1  or  2 , wherein the height of the iron bath corresponds to at least 20 times the diameter of the submerged tuyeres. 
     
     
       4. A process according to claim  1 , wherein the hot blast is blown at a speed between 0.4 and 0.8 Mach. 
     
     
       5. A process according to claim  1 , wherein the slags are granulated forming a slag with a glass content of more than 90%. 
     
     
       6. A process according to claim  1 , wherein coal in an amount of 60 to 350 kg/t slag along with nitrogen, as a carrier gas, in an amount of 6 to 9 Nm 3 /t slag as well as oxygen in an amount of 25 to 100 Nm 3 /t slag, optionally together with hydrocarbons for protecting the converter tuyeres, are passed through the iron bath. 
     
     
       7. A process according to claim  6 , wherein the nitrogen is fed in at a pressure of 7 to 10 bars. 
     
     
       8. A process according to claim  1 , wherein the hot blast is top-blown through lances located at the top of the converter, under a pressure of 0.8 to 1.2 bars, in amounts of 400 to 1200 Nm3/t slag. 
     
     
       9. A process according to claim  1 , wherein the process is controlled to limit the temperature of offgas from the converter to 1600 to 1800° C. 
     
     
       10. A process according to claim  1 , wherein fine ores in amounts ranging from 200 to 1500 kg/t steel slag are charged into the iron bath. 
     
     
       11. A process according to claim  1 , wherein the slag basicity of the steel slag is decreased prior to addition of the steel slag to the converter containing the iron bath, and 
       wherein the decrease in slag basicity occurs in a ladle.  
     
     
       12. A process according to claim  1 , wherein the SiO 2  carriers are simultaneously heated and purified in a melting cyclone, 
       wherein the melting cyclone is heated by offgases supplied from the converter, and  
       wherein the offgases comprise CO.  
     
     
       13. A process according to claim  12 , wherein the melting cyclone containing the SiO 2  carriers is supplemented with fine ores and/or Fe x O y  carriers so as to form fayalitic slag, and 
       wherein the fayalitic slag is mixed with the steel slag in a ladle prior to charging into the converter.  
     
     
       14. A process according to claim  12 , wherein the CO content of the converter offgases is burnt in the melting cyclone. 
     
     
       15. A process according to claim  12 , wherein Al 2 O 3  carriers are charged into the melting cyclone. 
     
     
       16. A process according to claim  1 , wherein the metal bath of the converter is drawn off and dephosphorized separately under reducing conditions by addition of at least one member selected from the group consisting of CaO, CaC 2 , metallic magnesium, metallic calcium and CaF 2 . 
     
     
       17. A process according to claim  6 , wherein the oxygen and hydrocarbons are fed in at a pressure ranging from 5 to 10 bars.